Radar marker circuit



. R. DARDEN, JR, EFAL RADAR 1H CIRCUIT Filed Feb. 16. 1949 FROMSWEEPCIRCUITS MPLIFIER ,3? r 24 if SIGNAL INPUT T GATTNG PULSE I 2 MASTER PIP GENERATOR Patented Aug. 8, 1950 2,517,635 RADAR MARKER CIRCUIT- Robert R. Darden, Jr., Solromar, Calm, and

Michael F. Kolodziei, Walthain, Mass., assi ore to Raytheon 'Manufacturing Company, Newton, Mass, a corporation of Delaware Application February 16, 1949, Serial No. 76,708

6 Claims. (01. ace-o) 1 This application relates to radar systems and more particularly to a circuit ina radar system whereby a'mark may be accurately displayed on a cathode ray tube to indicate the'relative direction of some'object which is fixed with respect to the indicator, for example, the bow of a ship on which the radar system is installed.

This mark which may hereafter be called ship?s head marker is desirable since the position of the ship's head on the face of a plan positioning indicator cathode ray tube .will vary with the compass bearing of the ship itself if the presentation used is relying on true target bearings. Therefore, it is an object of this invention to produce a mark which will accurately indicate :hedirection of the ships' head on the indicator ube.

A further obiecteof this invention is to devise a circuit which will produce a ships head mark- 7 er comprising a single radial line for high speeds of rotation of the antenna.

dal wave which in this particular embodiment I may have a frequency of 1140 cycles per second. This master oscillator is used to synchronize the various units of the radar system such as the transmitter and receiver sweep circuits. The sine wave emitted from the master oscillator I .is fed into a pip generator 2 which generates positive pips of a few-microseconds duration in synchronism with the sine wave input.

The pips are fed to the grid 3 of a normally cut-ofi tube 4 of a two-tube multivibrator. The cathode 5 of tube 4 is connected directly to the cathode 6 of theother tube of the multivibrator which is normally conductive. Both cathodes 5 and 6 are connected to ground through a cathode'resistor 8. The plate 9 of tube 4 is connected to a positive potential through a resistor l0, and the plate ll of tube 1 is connected to a positive potential through a series of resistors l2, I3 and M. The grid |5 of tube 1 is connected to a positive potential through a resistor l6, and to the plate 9 of the tube 4 through a condenser l1. The grid 3 of tube 4 is ordinarily maintained Well below cut-011?, that is, at a negative bias greater than the sum of in potential required to cut off tube 4' plus the amplitude .of the pips from generator 2,, by being connected through a grid resistor l8 to a tap on a voltage divider net- I work. This voltage divider network comprises a resistor l9, one end of which is connected to resistor I8 and the other end of which is connected to a negative potential of, for example, minus volts through two normally closed switches 20 and 2| in parallel. The junction between resistor l8 and resistor I9 is connected to ground through resistor 22 and resistor 23 in series. The junction between resistors 22 and 23 is connected to cathode 24 and 25 of two tubes 26 and 21, respectively, which constitute a second multivibrator. The values of resistors I9, 22 and 23, and the current drawn by the cathode 2B of the normally conducting tube 26 are such that the above-described bias is applied to the grid 3 of tube 4. In this condition the pips from the generator 2 are insufiicient to drive the grid 3 of tube 6 out of cut-oil.

The switches 20 and 2|, which are actuated by a cam 28 connected to the antenna such that they are both open at the same time once every revolution of the antenna, disconnect the resistor l9 from being directly applied to the negative potential. This cam 28 is attached directly to the antenna such that the switches which are opened in succession are both open when the antenna is pointed in a predetermined direction. This direction, for example, in the present embodiment is the direction wherein the antenna is pointed at the bow of the ship. When the switches 20 and 2| are both opened the resistor I9 is connected to the junction of two resistors 29 and 30 which constitute a voltage divider, one end of which is connected to ground and the other end of which is connected to the aforementioned source of negative potential. This voltage divider comprising resistors 29 and 30 applies a potential to the resistor [9 which is such that, with the tube 26 in its original conducting position, a lower bias potential is applied to the grid 3 of tube 4 through resistor l8. However, due to the current drawn through cathode resistor 8 by the tube the cathode 5 of tube 6 is maintained sufiiciently positive to still cut oii tube 4.

With this lower bias potential on grid 3, tube 4 may now be driven into conduction by the positive pips from pip generator 2. Current drawn through resistor ID by the conduction of tube 4 drops the potential of the plate 9 thus feeding a. negative voltage to the grid I5 of tube I through the condenser ll. This reduces the current "through the cathode resistor 3 which causes the tube 6' to conduct evenmore heavily. This action causes the tube 1 which was normally conducting heavily to be cut ofl. The tube I remains cut oil. until the condenser i1 charges, through the resistor l6 and the resistors 8 and III in parailel, sufliiciently to move the grid I! of tube I positive enough for the tube 1 to conduct.

by the values of condenser l1 and resistor l6 and is preferably somewhat greater than a quarter cycle of the master oscillator frequency. The pulse which occurs at the junction of the resistors l3 and It, in the form of a positive rectangular voltage wave, is fed through a condenser 31 to a gating circuit 32, the operation of which is more completely described in copending application Ser. No. 76,492, filed February 15, 1949. This gating circuit, which is synchronized to the master oscillator I, passes the pulse during a desired portion of the sweep cycle through an amplifier 33 to the grid 34 of an indicator tube 35.

In the present embodiment, the tube 36 is a cathode ray tube being operated as a plan position indicator, wherein the sweep of the electron beam controlled by the grid 33 starts from the center of the screen and moves radially outward at a rate such that it reaches the periphery of the screen in approximately a quarter cycle of the master oscillator frequency, and the gating circuit 32 is turned on by a suitable gating pulse to pass both incoming signals and the pulses appearing at the junction of the resistors l3 and it during this quarter cycle. These pulses are synchronized such that they occur at the beginning of the sweep with the result that a bright line appears on the screen extending from the center thereof to the outer edge whenever the multivibrator tube 4 is triggered. Since this triggering occurs only when both switches and 2| are open, when the antenna is pointed at the ship's how, the bright line will indicate the direction of the ship's head regardless oi the direction in which the ship is pointed.

Now then, since the antenna is rotated at a very rapid rate, for example, 60 R. P. M., it is difllcult to have both switches open for a duration that can be accurately controlled, due to the inherent inertia of any mechanical switching. Therefore, the multivibrator comprising tubes 6 and I might be triggered several times successively each time the switches 20 and 2! are open. This will produce a series of closely spaced radial lines on the screen whenever the switches 20 and 2| are open.

In order to produce only a single trace for the ship's head marker, a quenching circuit is triggered by the trailing edge of the pulse generated by the multivibrator tubes 4 and I which renders the tube 6 inoperative for a period of several cycles of the master oscillator, whereupon at least one switch 20 has closed, thus preventing the operation of the tube 6. This quenching I'llsconnectedtoapositivepotentialthroughs 36 and the plate 36 oi'tube- 23 isconnected toa positive potential through a resistor 63. The grid'3'l is also connected to theplate 4| oi tube 21 through a condenser 42. Thejplate llfloi' tube 21 is. to a positive potential through a resistor '43.] The grid 36 of tube 21 is connected toground. As aforementioned, the

cathodes 2t and 26b: the tubes are connected to the Junction between resistors 22 and 23 which iorm part or 'a voltage divider network feeding a bias voltage to the tube 6. The tube 2343 normally conducting since its grid 31 is connected to a positive potential through theresistor 33.- s The tube 21 is normally cut of! due to the voltage impressed on its cathode 26 by the current flow denser 36 to the grid 3'8 of tube 26. The grid of tube 26 through the common cathode resistor 23. when a positive pulse is ied through the condenser 36 to the grid 31 of tube 23, it is diflerentiated by the short time constant comprising the condenser 36 which is oi a low value and the relatively low grid to cathode resistance of.

the tube 26 which is drawing grid current. This produces a positive pip on the grid 31 due to the leading edge of the pulse and a negative pip due to the trailing edge or the pulse. The positive pip will have no effect since tube 26 is already conducting heavily. However. the negative pip generated by the trailing edge of the pulse will cut ofi the tube 26 and cause conduction of tube 21 due to the common cathode resistor 23 and the coupling between the plate ll of tube 21 and the grid 31 of tube 26 by condenser 62. The tube 26 will remain cut oil until the condenser 62 charges through resistor 38 and the resistor 33 parallel with cathode resistor 23 sumciently to allow tube 26 to begin to conduct whereupon the tubes return to their normal conditions wherein tube 26 is conducting heavily and tube 2'! is cut oil. Tube 21 will draw less current through the resistor 23 during its period of conduction than will tube 26 during its' period of conduction due to the fact that the grid 46 of the tube 21 is connected to ground rather than a positive potential. Therefore, when the grid 31 oftube 26 is triggered by the negative pip derived from the trailing edge of the pulse generated at plate ll of tube I, a negative pulse will appear across the cathode resistor 23. The width of this pulse,

is governed mainly by the values of condenser 42 and the resistor 38 and is made wider than the duration of the time during which both switches 20 and 2| are open. This negative pulse is applied through resistor 22 and resistor It to positively cut ed the grid 3 of tube 4 whereby the multivibrator is only triggered by the first of the pulses appearing on the grid 3 when the switches 20 and 2| are both open. Thus it may be seen that a single pulse will be fed through the gating circuit 32, when the switches 20 and 2| are both open, to produce a single line on the screen of the tube 36 for the ship's head marker.

This completes the description of the modification of the embodiment of the invention illustrated herein. However, many modifications will be apparent to persons skilled in the art; for example, any other source of pulses could be substituted tor the master oscillation and pip generator shown herein. Other types of pulse generator could be substituted for the multivibrators, and a single switch could be used rather than the two switches 20 and 2| in the antenna. Also, the marker pulse could be applied to any appropriate electrode of the cathode ray tube without passing through the gating circuit 32 and, negative pulses could be obtained from either plate 9 of tube 4 or cathodes 5 and 6 of tubes 4 and 1. In addition, switching could be accomplished by any suitable means, not necessarily a radar antenna, and the pulses obtained may be used for other purposesthan presentation on a plan position. indicator. Further, the values of circuit components may be varied considerably within the spirit and scope of this invention.

Accordingly, applicants do not wish to be limited by the specific details of this invention except as defined in the appended claims.

What is claimed is:

1. In a radar system having a directive antenna, and a cathode ray tube for the presentation of received signals, means for producing a mark on the screen of said cathode ray tube in dicative of a predetermined direction relative to said system, and means for insuring that said mark be present as a single trace, comprising means for disabling said mark producing means for a predetermined time immediately following generation of a single trace by said mark producing means, said disabling means comprising a pulse generator triggered by said mark producing means.

2. In a radar system having a directive antenna, and a cathode ray tube for the presentation of received signals, means for producing a mark on the screen of said cathode ray tube inv 4. In a radar system having a directive antenna, and a cathode ray tube for the presentation of received signals, means for producing a mark on the screen of said cathode ray tube indicative of a predetermined direction relative to said system, comprising a pulse generator, triggered by an antenna actuated switch once every revolution of said antenna, and means for indicative of a predetermined direction relative to said system, comprising a pulse generatontriggered by an antenna actuated switch, and means for insuring that said mark be present as a single trace, comprising means for disabling said mark producing means for a predetermined time immediately following generation of a single trace by said mark producing means, said disabling means comprising a pulse generator triggered by said mark producing means.

3. In a radar system having a directive antenna, and acathode ray tube for the presentation of received signals, means for producing a mark on the screen of said cathode ray tube indicative of a predetermined direction relative to said system, comprising a pulse generator, triggered by an antenna actuated switch once every revolution of said antenna, and means for insuring that said mark be present as a single trace, comprising means for disabling said mark producing means for a predetermined time immediately following generation of a single trace by said mark producing means, said disabling means comprising a pulse generator triggered by said mark producing means.

suring that said mark be resent as a single trace, comprising means for disabling said mark producing means for a predetermined time immediately following generation of a single trace by said mark producing means, said disabling means comprising a pulse generator triggered by means of the trailing edge of a pulse used to produce said mark.

5. In a radar system having a directive antenna, and a cathode ray tube for the presentation of received signals, means for producing a mark on the screen of said cathode ray tube indicative of a predetermined direction relative to said system, and means for insuring that said mark be present as a single trace, comprising means for disabling said mark producing means for a predetermined time immediately following generation of a single trace by said mark producing means, said disabling means comprising a pulse generator triggered by means of the trailing edge of a pulse used to produce said mark.

6. In ,a, radar system having a directive antenna, and a cathode ray tube for the presentation of received signals, means for producing a mark on the screen of said cathode ray tube indicative of a predetermined direction relative to said system, comprising a pulse generator triggered by an antenna actuated switch, and means for insuring that said mark be present as a single trace, comprising means for disabling said mark producing means for a predetermined time immediately following generation of a single trace by said mark producing means, said disabling means comprising a pulse generator triggered by means of the trailing edge of a pulse used to produce said mark.

ROBERT R. DARDEN, JR. MICHAEL F. KOLODZIEJ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 

